Mounted specimen



Jan. 17, 1950 R. s. RINGHEIM' MOUNTED SPECIMEN Filed July 10, 1945 Fig.1

, Fig.4.

INVENTOR. RIOHAR D $.R IN GH EIM ATTORNEY Fig.5.

Patented Jan. 17, 1950 MOUNTED SPECIMEN Richard S. Ringheim, SanGabriel, Caliih, assignor to the United States of America as representedby the United States Atomic Energy Commission Application July 10, 1945,Serial No. 604,280

Claims. 1

This invention relates to microscopy and more particularly to animproved mounting for a specimen to be examined under the microscope anda novel method of preparing such a mounted specimen. The mounting of thepresent invention is particularly useful in cases where it is desired toexamine a transverse section of a relatively thin sheet of material suchas, for example, a metal alloy sheet or a composite metal sheet. Howeverit will be understood that the present mounting is not limited to suchapplications.

In cases where it is desired to examine a transverse section of a thinsheet of material the specimen to be examined must be carefully mountedin order that the examination may accurately reveal the characteristicsof the specimen that it is desired to determine. It has previously beenproposed that such a specimen might be mounted in a molded plastic blockand a face of the block perpendicular to the plane of the specimenfinished on in such manner as to expose a transverse section of thespecimen for examination. In using this technique, however, a number ofdifficulties arise which render the results obtained by microscopicexamination somewhat misleading. In mounting the specimen, the piece ofmaterial to be examined may be enveloped in a suitable molding powderand pressure and heat applied to convert the molding powder into a solidblock containing the specimen. During this molding operation there is atendency for the specimen to tilt to a greater or lesser extent from thevertical position and thus when the face of the molded block is finishedoil the section of the specimen exposed is not a true transversesection, 1. e. it is not precisely perpendicular to the plane of thespecimen. Hence, if, for example, it is .ence to the accompanyingdrawing wherein desired to determine the relative dimensions of parts ofthe section these dimensions will be in error to the extent that thespecimen has tilted during the molding operation.

A further dlfllculty arises due to distortion of the specimen under thepressure that is normally applied during the moldin operation. It isevident that such pressures may easily alter the physical character ofthe specimen to such a degree as to produce a misleading appearanceunder the microscope.

It is accordingly an object of the present invention to provide animproved mounting for a specimen of a relatively thin sheet of materialwherein a transverse section of the specimen is exposed that ispreviseiy perpendicular to the plane or the specimen. I i

It is another object of the invention to provide 2 an improved method ofmounting a specimen for microscopic examination of a transverse sectionthereof.

It is still another object of the invention to provide a method ofmounting a specimen of a relatively thin sheet of material formicroscopic examination of a transverse section thereof in such mannerthat the specimen is firmly held in the mounting and precisely alignedwith respect to the face of the mounting that is to be examined.

Other objects of the invention will be in part obvious and in partpointed out hereinafter.

The many objects and advantages of the present invention may best beappreciated by refer- Fig. 1 is an isometric view of a specimen mountedbetween two supporting blanks of preferred construction Fig. 2 is anisometric view similar to Fig. 1 but showing an alternative supportingstructure;

Fig. 3 is a vertical cross-sectional view of a mold showing a specimenin position for incorporation in a plastic block;

Fig. 4 is a view similar to Fig. 3, but showing the molding powdercompressed around the spectmen;

Fig. 5 is a view similar to Fig. 4 but showing the specimen at the endof the molding operation embedded in a plastic block;

Fig. 6 is a transverse section taken on the line 6-6 of Fig. 5 andshowing the relative positions of the exposed faces of the specimen andsupporting blanks in the finished mounting; and

Fig. 7 is an isometric view of the finished plastic block with thespecimen and its supporting pieces encased therein.

In one of its broader aspects the present mounting comprises thecombination witha specimen of sheet material of a pair of reinforcingsupporting members or blanks fixed to opposite faces of the specimen,the specimen and blanks being encased in a molded block of plastic thathas one surface finished to expose a transverse section of the specimenfor microscopic. examination. The manner in which the present mountingis made may be best understood by reference to the accompanying drawing.Referring to the drawing and particularly to Figs. 1, 2 and 3 thenumeral Ill designates a cylindrical mold of well-known constructionhaving a platen l2 on which the object to be molded may be placed and aplunger l4 that fits snugly into the cylindrical mold Ill and is adaptedto be pressed downwardly to exert a desired pressure on the object to bemolded. Re-

ferring particularly to Fig. 1 a rectangular specimen lt'oi' the sheetof material to be examined is mounted between a pair of U-shapedsupporting pieces or blanks II and 20. The blank II (which may beidentical with the blank 20) comprises a pair of vertical legs I! and I1and a horizontal bridging member ii, the parts l5, l1 and. I9 being ofsquare cross-section. The legs I! and I1 and bridging member l8 define achannel or milled out portion 2| through which the side of the specimeni6 is exposed. The blanks l8 and 20 may be affixed to opposite faces ofthe specimen in any suitable manner and the particular method used willdepend to some extent upon the materials of which the specimen andblanks are constructed. It has been found that where the blanks l8 and20 are made of brass and the specimen 18 of nickel or copper that arubber cement may be desirably used for afiixing the blanks to thespecimen.

Care should be taken to make sure that the lower edge of the specimen I6is precisely aligned with the lower faces of the blanks Band 20. Thisalignment may be effected advantageously after the blanlm have beencemented to the specimen and before the cement has hardened by pressingthe blanks andspecimen downwardly on a fiat surface. The blanks are thenfirmly clamped to the specimen to prevent relative movement thereof andthe cement permitted to harden.

The clamps are then removed and the blanks and specimen placed on theplaten E2 in the manner indicated in Fig. 3. A suitable molding powdersuch as a Bakelite powder 22 is poured into the mold ID in an amountsufi'lcient to cover and envelop the specimen I6 and associated blanksl8 and 20. The plunger M is pressed downwardly to force the moldingpowder 22 against the specimen IS in such manner that the powdercompletely fills the channel 2i of the blank l8 and the correspondingchannel of blank 20. The relationship between the specimen and themolding powder at this stage of the process is illustrated in Fig. 4 ofthe drawing.

After the molding powder has been compressed around the mounted specimenthe mold is heated to cause the molding powder to be converted into asolid block. The condition of the block and specimen at the end of themolding operation is illustrated in Fig. 5 of the drawing.

The preferred molding schedule comprises heating the mold to about 65 C.at a pressure of the order of atmospheric pressure; then increasing thepressure to about 3000 pounds per square inch and increasing thetemperature to about 150 C. The temperature of 150 C. is maintained forapproximately five minutes after which the molded product is permittedto cool under pressure to about 100 C. to 110 C. at which temperaturethe mounting may be removed from the mold and permitted to cool to roomtemperature in the atmosphere.

At this point in the process the blanks l8 and 20 in the specimen l6 areembedded in a solidified mass of plastic. The blanks and specimen are sopositioned within the plastic block 22 that one edge of the specimen l6and the lower faces of the legs l5 and ll of blank i8 and correspondingfaces of the blank 20 are adjacent the lower surface 24 of the block 22.The surface 24 of block 22 is ground down to expose the transversesection of specimen I6 that it is desired to examine by any suitablemethod such as by utilizing well known grinding, lapping or polishingtechniques.

The appearance of the ground surface 24 is indicated in Fig. 6 whereinit designates the specimen to be examined and more particularly anexposed transverse section of the specimen that is preciselyperpendicular to the plane of the specimen. Abutting the specimen at itsends are exposed surfaces of the legs l5 and I! of the blank l8 andexposed surfaces of the legs H and I3 of the blank 20. As stated abovethe plastic during the molding operation passes throughthe channels inthe blanks I8 and 20 into contact with the specimen so that thetransverse section of the specimen I6 that is to be examined is boundedfor most of its length by the plastic material of the block 22. Thefinished mounted specimen is illustrated in Fig. '7 of the drawing.

The channelled construction of the blanks I0 and 20 which permits theplastic to be molded into intimate contact with the sides of thespecimen is an important feature of the present mounting. If the blanks18 and 20 were not milled out and the specimen I B were bounded by metalinstead of plastic less satisfactory results would be obtained. It isdifficult if not impossible to prevent small clearances between themetal of the specimen and the metal of the supporting blanks and thesetiny crevices tend to become filled with finely divided material duringthe grinding operation. Furthermore such crevices may permit deformationof the specimen during the grinding operation. With the presentconstruction, on the other hand, the plastic may be molded flush withthe side faces of the specimen along most of its length in such mannerthat there is no clearance between the specimen and plastic.

The blanks l8 and 20 perform several functions in the present mounting.In the first place they retain the specimen in vertical position duringthe molding operation so that when the surface 24 of the block 22 isground the exposed transverse section of the specimen I6 is preciselyperpendicular to the plane of the specimen. This accurate alignment ofthe specimen with respect to the block 22 is particularly importantwhere the specimen is a composite structure and it is desired to measurethe relative and absolute thicknesses of the various strata of thespecimen under the microscope, or in fact in any case where accuratemicro-measurements of the specimen are desired.

In some cases the structure of the specimen I 6 may be relativelydelicate and it is important to avoid distortion of the specimen duringthe molding operation in order that the examination of the specimenunder the microscope may yield an accurate picture of the structure ofthe specimen. The blanks l8 and 20 are of substantial assistance inpreventing such distortion. The principal stresses during molding arevertical stresses due to the downward pressure of the plunger I4 andthese stresses are almost entirely sustained by the supporting blanks.Furthermore the blanks serve to markedly diminish the horizontalstresses that would otherwise be exerted on the specimen. Thus only asmall fraction of the total molding stress is transmitted to thespecimen with the result that distortion of the specimen due to suchstresses is substantially reduced.

It is to be understood that the foregoing description is illustrativeonly and that many modifications may be made in the method of formingthe present mounting and in the mounting itself. For example Fig.2illustrates an alternative type of blank that may be used. In Fig. '2the specimen 26 is formed in the shape of a semi-circle and supported bythe blanks 28 and '30 which are in the form of half rings of rectangularcrosssection Any suitable type of powdered polymeric material may beused in the mold l0 and either a thermosetting or thermoplastic resinmay be used. The molding procedure will of course be modified slightlywhere other types of plastics are used but such modifications arecommonly known in the molding art. Thus for example methyl methacrylateplastic known as Lucite has been successfully used in place of Bakelitebut when Lucite is used it is desirable that the mounting be cooled tosay about 50 C. before it is ejected from the mold. In some cases it maybe desirable to etch the exposed section of the specimen before it isexamined under the microscope and in cases where the specimen is to beetched before examination Bakelite is preferable to Lucite because ofits greater resistance to acids. When, however, the nature of theexamination is such that no etching is required, a less resistantplastic such as Lucite may be satisfactorily used.

Since many embodiments might be made of the present invention and sincemany changes might be made in the embodiment described, it is to beunderstood that the foregoing description is to be interpreted asillustrative only and not in a limiting sense.

I claim:

1. A mounted specimen of a relatively thin sheet material having atransverse section exposed for microscopic examination, comprising, incombination with said specimen, a pair of reinforcing blanks aflixed toopposite faces of said specimen and a molded block of plastic encasingsaid specimen and blanks, said block having one surface finished toexpose a transverse section of said specimen for microscopicexamination.

2. A mounted specimen of a relatively thin sheet material having atransverse section exposed for microscopic examination, comprising, incombination with said specimen, a pair of reinforcing blanks affixed toopposite faces of said specimen. said blanks being so affixed to saidspecimen that corresponding faces of said two blanks are flush with saidtransverse section, and a molded'block of plastic encasing said specimenand blanks, said block having one surface finished to expose atransverse section of said specimen for microscopic examination.

3. A mounted specimen sheet material having a transverse section exposedfor microscopic examination, comprising, in combination with saidspecimen, a pair of channelled blanks affixed to opposite faces of saidspecimen and a molded block of plastic encasing said specimen andblanks, said block having one surface finished to expose a transversesection of said specimen and said plastic extending through saidchannels into contact with said specimen.

of a. relatively thin,

a 6 4. A mounted specimen of a relatively thin sheet material having atransverse section exposed for microscopic examination, comprising, incombination with said specimen, a pair of channelled reinforcing blanksaffixed to opposite faces of said specimen, said reinforcing blanksbeing so aflixed to said specimen that said channels are adjacent saidtransverse section,'and a molded block of plastic encasing said specimenand blanks, said block having one surface thereof finished to exposesaid transverse section and said plastic extending through the channelsin said blanksto points adjacent said transverse section;

5. A mounted specimen of a relatively thin sheet material having atransverse section exposed for microscopic examination, comprising, incombination with said specimen, a pair of U-shaped blanks aflixed toopposite faces of said specimen, said blanks being so aifixed to saidspecimen that the end surfaces of said blanks are flush with saidtransverse section, and a molded block of plastic encasing said specimenand blanks, said block having one surface finished to expose saidtransverse section for microscopic examination.

RICHARD S. RINGHEHMI.

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